Chapter 3. Introduction to Red Hat Virtualization Products and Features

This chapter introduces the main virtualization products and features available in Red Hat Enterprise Linux.

3.1. KVM and Virtualization in Red Hat Enterprise Linux

KVM (Kernel-based Virtual Machine) is a full virtualization solution for Linux on AMD64 and Intel 64 hardware. It is built into the standard Red Hat Enterprise Linux 6 kernel and integrated with the Quick Emulator (QEMU), and it can run multiple, guest operating systems. The KVM hypervisor in Red Hat Enterprise Linux is managed with the libvirt API, and tools built for libvirt (such as virt-manager and virsh). Virtual machines are executed and run as multi-threaded Linux processes, controlled by these tools.
KVM architecture

Figure 3.1. KVM architecture

Virtualization features supported by KVM on Red Hat Enterprise 6 include the following:
Overcommitting
The KVM hypervisor supports overcommitting of system resources. Overcommitting means allocating more virtualized CPUs or memory than the available resources on the system, so the resources can be dynamically swapped when required by one guest and not used by another. This can improve how efficiently guests use the resources of the host, and can make it possible for the user to require fewer hosts.

Important

Overcommitting involves possible risks to system stability. For more information on overcommitting with KVM, and the precautions that should be taken, refer to the Red Hat Enterprise Linux 6 Virtualization Administration Guide.
KSM
Kernel Same-page Merging (KSM), used by the KVM hypervisor, makes it possible for KVM guests to share identical memory pages. These shared pages are usually common libraries or other identical, high-use data. KSM allows for greater guest density of identical or similar guest operating systems by avoiding memory duplication.

Note

For more information on KSM, refer to the Red Hat Enterprise Linux 6 Virtualization Administration Guide.
QEMU guest agent
The QEMU guest agent runs on the guest operating system and enables the host machine to issue commands to the guest operating system.

Note

For more information on the QEMU guest agent, refer to the Red Hat Enterprise Linux 6 Virtualization Host Configuration and Guest Installation Guide.
Hyper-V Enlightenment
KVM in Red Hat Enterprise Linux 6.5 and later implements several Hyper-V compatible functions that are used by Windows guests to improve performance and stability, enabling Windows guests to perform as if they were running on a Microsoft Hyper-V hypervisor.

Note

For more information on Hyper-V Enlightenment, refer to the Red Hat Enterprise Linux 6 Virtualization Host Configuration and Guest Installation Guide.
KVM guest virtual machine compatibility
Red Hat Enterprise Linux 6 servers have certain support limits.
The following URLs explain the processor and memory amount limitations for Red Hat Enterprise Linux:
For a complete chart of supported operating systems and host and guest combinations refer to Red Hat Customer Portal.

Note

To verify whether your processor supports virtualization extensions and for information on enabling virtualization extensions if they are disabled, refer to the Red Hat Enterprise Linux 6 Virtualization Administration Guide.